The present invention relates to lithography, and more particular to a process for developing high-aspect ratio resist profiles using a developer which includes no toxic chemicals.
In the field of semiconductor and magnetic device manufacturing, lithography is generally used to provide a pattern to a substrate needing patterning. Typically, the substrate is patterned by steps which include: applying a resist, exposing the resist to an energy source, developing the patterned resist using a suitable resist developer so as to expose a portion of the underlying substrate, and optionally, etching the exposed surface of the substrate by reactive-ion etching (RIE) or other suitable dry etching processes. The processing steps including resist application, exposure and development are referred to as xe2x80x9clithographyxe2x80x9d. Although various resist profiles are known, high-aspect ratio resist profiles are typically used in fabricating masks, field effect transistors (FETs), micro-electrochemical systems (MEMS) and thin-film heads for magnetic disks. High-aspect ratio profiles are most notable for thin film heads because the writing yoke for the thin-film heads requires a tall, narrow metal line which is normally plated through a resist pattern. The term xe2x80x9chigh-aspect ratioxe2x80x9d as used herein denotes a resist profile whose depth to width ratio is greater than 5.
In the prior art, numerous solvents or solvent systems comprising one or more organic compounds have been described which are capable of developing high-aspect ratio resist profiles in non-aqueous developable, polymeric resists, i.e., solvent developable resists. The prior art developers are typically composed of one or more toxic, e.g., carcinogenic or mutagenic, chemicals such as methylisobutylketone (MIBK), morpholine, toluene, chlorobenzene and butoxyethoxyethanol.
In addition to being toxic, prior art resist developers may cause excess resist swelling. Excess resist swelling during resist development is undesirable since it causes narrow lines to close at the resist surface, e.g., a pinch-off phenomenon occurs. A second problem caused by excess resist swelling during resist development is resist cracking. That is, solvent entering the resist will expand the volume of the resist film; however, the film must remain firmly adhered to the substrate. Stress relief caused by this swelling commonly occurs through cracking of the film, usually at the corners of the pattern.
In view of the drawbacks mentioned above in regard to prior art resist developers, there is a continued need for providing a new and improved resist developer that is does not cause excess swelling of the resist, does not cause any substantial cracking of the resist during resist development, yet is capable of developing high-aspect ratio profiles in non-aqueous developable resists.
One object of the present invention is to provide a method of fabricating high-aspect ratio profiles in nonaqueous developable, polymeric resists.
Another object of the present invention is to provide a method of fabricating high-aspect ratio resist profiles wherein the resist developer solution is non-toxic, i.e., non-carcinogenic or non-mutagenic.
A further object of the present invention is to provide a method of fabricating high-aspect ratio resist profiles in which the resist developer does not cause excess resist swelling and cracking during resist development.
A yet further object of the present invention is to provide high-aspect ratio resist profiles for fabricating masks, FETs, MEMS and thin film heads for magnetic disks.
These and other objects and advantages are obtained in the present invention by utilizing a resist developer which includes an alcohol/water mixture. Specifically, the method of the present invention comprises the steps of:
(a) applying a non-aqueous developable, polymeric resist to a surface of a substrate needing patterning;
(b) forming a high-aspect ratio pattern in said nonaqueous developable, polymeric resist by exposing the same to an energy beam; and
(c) developing the high-aspect ratio pattern in said nonaqueous developable, polymeric resist using an alcohol/water mixture.
In one embodiment of the present invention, the high-aspect ratio pattern is then transferred to the substrate by utilizing a conventional etching process such as RIE and numerous materials such as dielectrics, conductors and magnetic materials may be formed in the patterned region of the substrate and thereafter the non-aqueous developable, polymeric resist is stripped utilizing a conventional stripping process.
In another embodiment of the present invention, the developed resist containing the high-aspect ratio resist pattern is used as a plating mask wherein various materials can be formed therein.